Ultra wideband technology is distinguished from narrowband and spread spectrum technologies in the sense that the bandwidth of an ultra wideband type signal is typically between about 25% to 100% of the central frequency. Moreover, instead of transmitting a continuous carrier modulated with information or with information combined with a spreading code, which determines the bandwidth of the signal, ultra wideband technology involves transmission of a series of very narrow pulses. For example, these pulses may take the form of a single cycle having a pulse width of less than 1 ns. These pulses are extremely short in the time domain, and when transformed into the frequency domain, lead to the obtaining of the ultra wideband spectrum that is characteristic of UWB technology.
In UWB technology, the information on the signal can be coded, for example, by a modulation technique called pulse position modulation (PPM). In other words, the information coding is carried out by varying the instant of transmission of individual pulses. More specifically, the pulse train is transmitted at a frequency of repetition that can extend up to several tens of MHz. Each pulse is transmitted in a window of predetermined length, for example 50 ns. Compared to a theoretical position of transmission, the pulse is then ahead or delayed, enabling a 0 or a 1 to be coded. More than two values can also be coded using more than two positions offset relative to the reference position. It is even possible to superimpose a BPSK type modulation onto this position modulation.
On receiving the transmitted signal, these pulses must therefore be detected for determining, if necessary, their position if a PPM type modulation has been used. Until now, this detection of pulses is carried out using an analog correlator, which requires a relatively complex hardware implementation.